Installing win10 problems, out of solutions/alternatives...

Hi
Sorry about the long description, but want to make sure I haven’t missed any detail along the process and to inform people which alternatives have been tried.

I have been experiencing a lot of problems with the win10 installation. After a lot of work I managed to fix my main computer (was probably dells fault (network drivers)), but when helping my step dad with his laptop I can’t seem to get it up and running.

The laptop is a «Toshiba Satellite L750 – 1T9» with win7 pre installed. (specs in "my system specs" below)

He tried updating to win10, but when the wifi didnt work in win10 he (not being technical) decided to restore it to win7. This recovery failed and after this, the computer got stuck in a install win 10 loop. He then asked me for help to recover his files and to try to get windows up and running. I managed to recover the files with a HDD docking, and from there on it has just been problem after problem.
I first tried using the repair / install win10 / boot(F12 startup), but the computer just kept giving the blue screen with the «installation failed, need to restart» or something like that no matter what option I chose. I thought there might be a problem with the installation file so I tired formatting the disk and install win10 form an usb-device (formatted) with the iso file provided from Microsoft (by using the media creation tool), but his solution led to the same result(loop). I than tried connecting the hdd to a computer with docking again and wiping all partitions visible, in case some old files were disturbing the installation. Still the same loop result.

A couple of weeks later (yesterday), I tried to attack the problem from a new angle, and switched the HDD’s from my laptop to my step dads Toshiba. The Toshiba (at this point with my functioning win10 dell HDD) gave me the «Checking media(failed)» message, than showed the dell logo(startup) but failed to start win10.
I than tried to installing win10 on the Toshiba HDD(formatted again) from my main(dell) laptop by using a new USB-stick with a freshly downloaded iso file. This didn’t work at first, but after deleting all partions of the HDD and making new ones, the installation process worked just fine, and windows was running smoothly, without any problems.
I than tried switching back the HDD’s, but the Toshiba still would not launch windows, even tho it had worked perfectly fine on the dell. When I start the Toshiba it gives me the “For artheros Ethernet controller….. check cable connection…..no bootable device” message (tries booting from network card). My first thought was that the boot order was switched up so I went in to startup settings menu (F2 on startup) but the order was fine (1.hdd, 2.ODD, 3.Network). I also tried setting settings to default, connecting Ethernet cable, changing settings etc, but it still tries booting from network, and does not boot from hdd (tried re-insering it), and this is where I am at atm. I have tried hitting 0, esc, etc on startup (to start Toshiba software), but it just makes the computer beep without anything else happening.

I also tried downloading win7 iso file, but this required serial, and when entering the key I get a message saying that my serial is for a fabric installed version of win7 and that I have to contact them(Toshiba) for installation cd. Have not went any further in trying to obtain/install win7.
Have been searching the web for several hours, but cannot seem to find the cause/solution.
As mentioned above I know the HDD is functioning since I inserted it in my dell, installed win10 and ran it without problems, but the Toshiba no won’t even read it, goes straight to network boot.

Any ideas on what might cause this / how I can fix it or what I can try to get windows up and running with another alternative?